Currently, several series of casting brass alloys are in widespread use, for example, the Cu—Zn series, Cu—Zn—Si series, Cu—Zn—Al series. Each series includes lead-containing alloys. Lead-containing casting brass alloys have excellent cuttability, castability and low cost. However, these alloys harm the environment and the human body in the process of their production and usage. Furthermore, lead-containing brass alloys have poor weldability.
The harmfulness of lead to the environment and the human body is of great concern. Over the past 15 years, many patents for lead-free or low lead free-cutting brass alloys have been published or granted in the US, China, Japan, Germany and Korea. There are twenty bismuth brass alloys (CN2005100504254, CN2003101091620, CN021219915, CN941926133, CN931200644, CN2007100674803, CN2005800014925, CN2008100659066, U.S. Pat. Nos. 6,599,378, 5,653,827, 5,288,458, 5,409,552, 5,630,984, 5,614,038, US 2004/0159375, JP2000239765, JP2002003967, JP2001059123, JP2006322059, JP2003119527), ten silicon brass alloys (CN2004100891500, CN2004100042937, CN2005800194114, CN2005800464607, US20070169854, US 20020069942, US 20070062615, US 20050247381, JP2000336441, JP2001064742), seven tin brass alloys (CN2004100042922, CN031551777, CN2006100056892, US 2004241038, US20040159375, JP2000087158, JP2003147460, two antimony brass alloys (CN2007100708034, CN2004100158365), one magnesium brass alloy (CN2007100359122), one aluminum brass alloy (U.S. Pat. No. 3,773,504) and one tellurium brass alloy (CN2004100222446) disclosed in the prior art. These references primarily disclose lead-free free-cutting deformation brass alloys. Few, if any, references disclose lead-free alloys that are applicable in castings and/or low pressure die casting.
Published lead-free or low lead free-cutting casting bismuth brass alloys include UNS C89550 (high zinc, lead-free), UNS C89837 (low zinc, high copper, lead-free), UNS C89510 and UNS C89520 (low zinc, high copper, lead-free), and FR CuZn39Bi1Al. These alloys contain small amount of Sn and Se. The bismuth brass alloys disclosed by some references add expensive Se and Sn and even more expensive Te and In to change the dispersion of Bi in the grain boundary from continuous film to discontinuous particle. This has the beneficial effect of decreasing the hot and cold brittleness of the bismuth brass alloy.
One disadvantage of prior art bismuth-brass alloys is that the metals Bi, Sn, Ni, Se, Te and In are relatively expensive. Another disadvantage of prior art bismuth brass alloys is that they have poor castability and weldability. Accordingly, castings made of bismuth brass alloys by low pressure die casting are prone to cracking, resulting in a low overall yield. Also, castings made of bismuth brass alloys by brazing are also prone to cracking in weld and heat-affected zones. Furthermore, the forging temperature range is narrow. These are some of the obstacles presented by bismuth brass alloys. There is a need for mass-produced faucet bodies and valve bodies made from lead-free free-cutting brass, by low pressure die casting and weld-forming and by forging and weld-forming, respectively. Since bismuth is relatively rare and expensive, and requires improvements in technological properties such as castability and weldability beyond what is currently known in the art, the application and development potential of bismuth brass alloy is limited.
Current casting silicon brass alloys usually contain Pb. These alloys are highly prone to be hot cracked in the process of low pressure die casting. Furthermore, the Pb release will exceed the requirement of NSF61 standard.
Nowadays, research and development of lead-free or low lead free-cutting silicon brass alloys is typically based on brass alloys with low zinc and high copper. These alloys rely on increasing the relative ratio of hard and brittle γ phase in the alloy to ensure the free-cuttability of the alloy. This approach sacrifices the plasticity of the alloy and is detrimental to casting formings and process formings. Furthermore, as the content of Cu is high, the cost of materials is high. At present, many prior art silicon brass alloys are deformation alloys. The content of zinc and copper in these alloys overlap, and most are silicon brass alloys with high copper. Typically, there is little discussion or disclosure of the castability of the alloys, or their suitability for low pressure die casting.
For example, two antimony brass alloys prior arts (CN2007100708034 and CN2004100158365) issued to Zhang et al. both disclosed Sb as one of the main elements of the alloys. But Zhang et al. do not discuss or disclose the castability of the alloy, particularly the castability applied on low pressure die casting. Furthermore, the Sb release of these alloys into the water may exceed the NSF/ANSI61-2007 standard and should not be used for drinking water supply system applications.
The internal construction of faucet bodies is very complex. The faucet bodies typically are hollow castings with slim walls whose thickness can vary. The cooling intensity of the mold for low pressure die casting is large. The alloy must have excellent castability, especially excellent mold filling performance and hot crack resistance. These kinds of castings also are subjected to cutting processes including, for example, sawing, lathing, milling, drilling and polishing. All these processes require the alloy to have excellent cuttability. There is a need for mass-produced faucets made by casting and weld molding, and for valves made by forging and weld molding. These applications require the alloys to have excellent weldability. Additionally, standards for drinking water, such as NSF/ANSI61-2007 strictly restrict the amount of elements such as Sb, Pb, Cd, and As that can be released into the water. For example, under the NSF/ANSI61-2007 standard, the maximum acceptable release amount of Sb and Pb is 0.6 ug/L and 1.5 ug/L, respectively. If the Sb content in the brass alloy exceeds 0.2 wt %, the amount of Sb release into the water will exceed 0.6 ug/L. Thus, some antimony brass alloys are not suitable for use in drinking water system installations.